The present invention relates to optical exposure systems and optical process for aligning optical alignment layers and liquid crystals with light.
Liquid crystal displays (LCDs) find application in many areas of information display, including instrument controls, watches, portable computers, desk top computer monitors, LCD televisions and LCD projectors. Most LCD devices employ an LCD panel that has a layer of liquid crystal material disposed between a pair of substrates. The inner surface of at least one of the substrates is an alignment surface for aligning the liquid crystal molecules in the absence of an applied electric field. Commonly, the alignment surface is a polymeric alignment layer. In some displays, the direction of alignment of the alignment layer is established in a mechanical buffing process wherein the polymer layer is buffed with a cloth or other fibrous material. The liquid crystal medium contacting the buffed surface typically aligns parallel to the mechanical buffing direction.
Alternatively, an alignment layer comprising anisotropically absorbing molecules can be exposed to polarized UV light. Such exposure aligns the molecules of the alignment layer which can then be used to align a liquid crystal medium. This type of alignment layer is referred to herein as an exposed alignment layer.
In many LCDs, the alignment layer not only aligns the liquid crystal (LC) molecules, but also imparts a pre-tilt to the molecules. The LC molecules that contact an alignment layer with pre-tilt are aligned in a direction parallel to a particular direction, for example the buffing direction when using a buffed alignment layer, but the LC molecules need not be aligned parallel to the substrate. For example, the LC molecules may be tilted from the plane of the substrate by a few degrees. Many types of LCD require that the alignment layer include a pre-tilt for optimum performance. An exposed alignment layer can be given a pre-tilt by altering the angle of incidence of the UV light when exposing the alignment layer.